A turret is one of two knobs in the outside center part of a riflescope body. Turrets are marked in increments and are used to adjust elevation and windage for points of impact change. Conventional turrets have markings on them that indicate how many clicks of adjustment have been dialed in on the turret, or an angular deviation, or a distance compensation for a given cartridge. A click is one tactile adjustment increment on the windage or elevation turret of a scope.
In order to achieve accurate sighting of objects at greater distances, the downward acceleration on the projectile imparted by gravity is of greater significance. The effect of gravity on a projectile in flight is often referred to as bullet drop because it causes the bullet to drop from the shooter's line of sight. For accuracy at longer distances, the sighting components of a gun must compensate for the effect of bullet drop. An adjustment to the angular position of the rifle scope relative to the rifle barrel is made using the elevation turret to compensate for bullet drop.
Conventional elevation turrets allow for multiple rotations in order to enable the scope to compensate for longer-range targets. Unfortunately, conventional turrets typically omit at least one of the following functions: adjustment stops that prevent adjustment of the elevation and windage turrets beyond preset amounts, rotation indicator/counter, or turret locking. As a result, users of conventional turrets may lose track of how many rotations are dialed in if he or she does not carefully count the number of rotations both while dialing away from the zero point and when dialing towards the zero point even when the turret's markings are visible. Furthermore, turrets can be easily humped, and in dark conditions where it may be difficult to see the turret markings, the user may not realize the turrets have been inadvertently adjusted if the turret omits a locking mechanism.
Another difficulty with existing rifle scopes is that certain operating conditions require the user to remember both how many clicks and the direction of rotation needed to return the elevation turret to its zero point from a different setting. When light conditions are poor, such as at twilight, night, or in darkened rooms of buildings, or if it is difficult for the user to hear or feel the clicks, it is very easy for the user to lose track of what adjustment is needed to return to the zero point. Under such conditions, the markings may not be sufficiently visible and the absence of a tactile rotation indicator is keenly felt. This is particularly significant for police and military users of firearms, who in the course of their duties may very likely be confronted with a threat under poor lighting conditions. In addition, hunters may hunt at twilight or in deep shade.
Because of the need for compact riflescope components, markings are necessarily small, making them difficult to read under borderline conditions. White this may be a concern when making fine adjustments, it is of greater concern when a user must make large changes involving several revolutions of a knob, which may lead to an error in the number of revolutions made.
Therefore, a need exists for a new and improved rifle scope with adjustment stops that prevents adjustment of the elevation and windage turrets beyond preset amounts. There is also a need for visual and tactile indication of how many rotations have been dialed in on the elevation turret. Finally, there is a need for a turret locking mechanism so the user can be assured that the turret is still in its last used position. In this regard, the various embodiments of the present invention substantially fulfill at least some of these needs. In this respect, the spiral cam mechanism according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in doing so provides an apparatus primarily developed for the purpose of preventing adjustment of a turret beyond a preset amount, giving the user an indication of how many rotations have been dialed on the turret, and giving the user the ability to lock the turret.